Sidecar will work with MiSTer - Case Universal v5.2.
https://www.youtube.com/watch?v=zALJqBP9OZc
Slowly iterating the design. Sorry for taking so long.

Today I did my first physical testing of the add-on case.
Not quite there yet ...
so close.. USB cut-outs are too small and have to be slightly enlarged in the next version. Also the panel bracket idea is not yet working. Maybe needs another re-design. I will keep you updated.

Edit: It is released now:
https://www.thingiverse.com/thing:3025189
https://youtu.be/eQElAyntNXY